Starch is an important ingredient for the food industry and is very commonly used in a great multiplicity of food applications and food production processes. Natural, non-modified starch, known by skilled persons in the art as “native starch”, is sometimes used as such but has several disadvantages.
The primary function of starch in food applications is as thickening agent with a view to provide the requested viscosity, texture and mouth feel of food products. The texture and viscosity property are built up by hydration of the granular starch achieved when the granular starch is heated in an aqueous suspension. The granular starch absorbs water when the temperature is increased above the gelatinization temperature, i.e. the starch granule is being hydrated and swollen and its viscosity is considerably increased. In the case of using native starch the hydrated and swollen starch granules are not stable and, consequently, if the temperature is kept for longer time or is increased to higher temperatures the viscosity will reach its so called “peak viscosity”. Accordingly, the granular shape will be disrupted and disintegrates. The viscosity will be significantly reduced. Besides the reduced viscosity, another drawback will be an unpleasant long and cohesive texture.
As a result of the above-mentioned problem the most important parameters to control or to avoid are high temperatures, shear forces, and, particularly, acidic conditions. A result when the cook goes beyond the “peak viscosity” is a breakdown of the granular structure. Instead, it is desirable to change the starch property so that the viscosity is stable or even increase over time, thus avoiding viscosity decrease and granular breakdown when treated under high heat, strong shear force, and/or acidic conditions. This maintains hydrated highly swollen but intact, hydrated starch granules.
The requested effect is often referred to as increased starch robustness. Thus, the granular starch is more resistant to high temperatures, longer heating times, strong shear forces, and acidic conditions or combinations of those parameters.
The most commonly used method of modification to give starch increased process tolerance is to use the technique known as chemical cross-linking. Chemical cross-linking inhibits the starch granule, so that when it is heated in water its swelling is inhibited. If the level of cross-linking is too low a continued heating combined with strong physical force or not will end up in a total or partial starch solution. Chemical cross-linking prevents granular breakdown under such treatments. The chemical cross-linking is achieved by substituting the starch with a bi-functional reagent, resulting in a covalent bond between the starch molecules. This can be done with certain approved methods and chemicals, e.g. phosphorus oxychloride, STMP (sodium trimetaphosphate), adipic-acetic mixed anhydride, and epichlorohydrin. The different approved methods for chemical cross-linking are well described in the literature and are commonly used in the starch industry. In practice, this means that by cross-linking of the starch granule it will be capable of maintaining its granular integrity when exposed to temperatures and high shear force or at high temperatures without or together with a low degree of shear. The higher the degree of cross-linking, the more robust the starch will be against high temperature, shear forces and acidic conditions or combinations of those parameters.
In practice, these cross-linking techniques for modifying the property of the swelling of the starch granule can be adapted to the application and the process which the starch is to be used in, so that optimal properties in the form of viscosity and texture are obtained due to the starch as such.
In the food industry, there is a great desire to replace chemically modified starches with starches that are not chemically modified, due to the trend to go “natural” among the food ingredients. The starch shall still have equal properties as the chemically modified ones.
Non-chemical inhibition of starch granules can be performed with dry heat inhibition, also called alkaline dry roasting, similar to the so called British Gums. In this method the starch is subjected to high temperatures in an almost totally moisture free condition in combination with an alkaline pH, which is reached by addition of e.g. sodium hydroxide or soda. Temperatures of 120-160° C. at a pH of 8-11 and a reaction time of 2-120 hours give different inhibition levels. This technique is well known and disclosed in the literature (Cross-linking of starch by Alkali Roasting, Journal of Applied Polymer Science Vol. 11 PP 1283-1288 (1967); IRVIN MARTIN, National Starch & Chemical Corporation) and also in several patents (U.S. Pat. No. 8,268,989 B2; EP 0 721 471; EP 1 0382 882; U.S. Pat. Nos. 3,977,897; 4,303,451; Japanese Patent No 61-254602; U.S. Pat. Nos. 4,303,452; and 3,490,917).
The problem with heat inhibition of starch is that side reactions give an undesirable taste and color to the starch. A discoloration of the starch occurs at temperatures above approximately 130° C. To avoid problems with the side reactions the temperature can be reduced, but this causes the reaction time to be prolonged, thereby increasing the production cost significantly. Furthermore, the heat inhibition technology requires high energy costs and high investment costs.
It is further known that a weak inhibition can be achieved by subjecting the starch granule to low concentrations of a bleaching agent, i.e. an oxidant (oxidizing agent) at an alkaline pH together with so called oxidation modifiers, which are different nitrogen containing compounds. In some cases the residual protein in the starch granule remaining after extraction can be used as the oxidation modifiers, but it generally needs less pure starches than nowadays commercial starches has, i.e. above 0.4% protein content of starch dry matter. This inhibition technology is known and is disclosed in U.S. Pat. No. 2,317,752 and in the UK Patent Application GB 2506695. However, the latter two methods of inhibiting starch can be performed only to a limited inhibition level. If higher levels of oxidants are added the starch will instead be oxidized, leading to a de-polymerization which results in reduced viscosity and easier disruption of the granular structure during cooking.
It is also known that inhibition of granular starch can be achieved by combining an oxidant and the amino acid glycine. This process is disclosed in U.S. Pat. No. 3,463,668. However, this method results in an unstable, temporarily inhibition and is thereby not capable of replacing chemically cross-linked granular starches in the food industry.
Accordingly, there is a need to develop a method for inhibiting starch to higher levels, i.e. a method which results in inhibited starches with improved properties like taste, smell and color, and which is more cost effective than traditional techniques to produce and overcomes the drawbacks in earlier described techniques. There is also a need for an inhibited food starch which is stable during the storage time in the warehouse and which has improved organoleptic properties, and also the food products produced there from.